All manner of ideas have been given: finite durability, decay, increasing repairs. All of these were intended to... I forgot why. I think it had something to do with crafting? Yea, that's it, if our gear breaks all the time we'd use crafting more and run older raids more and everyone would be so much happier.
What a stupid idea! No, not because people dislike loss. Instead the problem is that it doesn't go far enough.
Gear should be your enemy.
Let's take the One Ring as an example. The first time Bilbo put it on, not much of a problem. It saved his life. Poof, invisible. But repeated use gave him long life, stretched life, like butter spread over too much bread. He was lucky!
Isildor was attacked by orcs and his attempt to use it to escape was thwarted when it grew too big for his finger and slipped off. He was betrayed by the ring.
Smeagol (Gollum) fared little better. His life was stretched, his mind corrupted, all hobbitity driven from him (or was it?). But at least the ring did not get him killed. No, instead it simply abandoned him in the bottom of a goblin-infested mountain. And drove him to murder and treachery, but the greatest of loyalty, for he could not break his word upon his Precious.
Frodo learned that the Ring does not give universal invisibility, but instead makes him more visible (and able to see), the terrible Ringwraiths: victims of other corrupting rings (I oversimplify their story). Even worse, the Eye of Sauron has no problem finding him in the shadow realm.
Strangely, Gandalf claims that wearing the ring too long will cause the person to fade. A strange claim because he has no actual examples. Sauron, Isildor, Gollum, Bilbo, Frodo. Beside a few people who briefly touched it, these are all the bearers and none had faded away. Gandalf did say it takes a very long time, but how long? He clearly knows more than us to be able to predict such an effect.
Our loot does not betray us. It does not abandon us in hour of need. It does not slip off or render us vulnerable to our worst foes. Perhaps it should!
Of course not all armor, because that would be a huge hassle resulting in us running around mostly naked. Then again, female armor suggests we already are mostly naked. But that's beside the point. Betraying items would be unusual, both in rarity and in slots. Rings, necklaces, trinkets. These would be items of great power, but which would be needed to be controlled or destroyed at the wrong time.
Think of Quel'dalar. At one point during its cleansing and renewal it attacks the player, but by defeating it we become stronger. Why do we not do this more often? Most loot is rather boring.
Imagine a necklace which grants great power, but which will eventually choke you to death, reducing stamina. When I say eventually I mean weeks of game time, so there is no great rush and any player with time to get the neck will have time to save themselves, but it could not be entirely ignored. Maybe the neck would need to be cleansed or maybe destroyed or maybe given away to a greedy enemy as a trap. Perhaps the player can choose a path with significantly different rewards for each.
Gear is mostly non-interactive. We get it and then we have it. We click on a vendor when we get something better. For the most part it is like auto-attack. While that's certainly a solid foundation, I'd hate to have no auto-attack or to spend every other day fighting my latest evil boots, it is boring.
Or maybe we just suck at RP and are incapable of sensing adventure. A random encounter with trolls granted Bilbo's party several powerful and legendary swords. Taunting a dragon, which was then killed by someone else completely out of sight, gave Bilbo his mithril armor and everyone involved ridiculous amounts of gold. The One Ring was found by Bilbo getting lost in a cave and playing riddles. Perhaps by comparison our invasion of Ulduar and Icecrown Citadel is epic and heroic and the boring nature of loot is all in our heads.
Our loot does not betray us. It does not abandon us in hour of need. It does not slip off or render us vulnerable to our worst foes. But it is... our Precious...
6 hours ago